uml/state-machine-diagram.md

@@ -16,7 +16,18 @@ UML state diagrams use the following notations:
 - *States* are denoted as rectangles with rounded corners and a name.
 "A State models a situation in the execution [...] during which some invariant condition holds.
 In most cases this condition is not explicitly defined, but is implied, usually through the name associated with the State." (UML Spec 2.5, S.348/306)
-For example: "Ringing" or "Dialing" are common states when modeling the state machine for a telephone.
+For example: "Ringing" or "Dialing" are common states when modeling the state machine for a telephone. *States* may contain (optional) internal behavior that is sequentially executed after entering the state:
+
+  - *Entry* actions are executed and completed when the *state* has been entered.
+  - *Do* actions are executed when the *state* has been entered and always after a potential *entry* action is completed.
+*Do* actions are executed until they are completed or until the *state* is left.
+Therefore, their execution may be interrupted.
+  - *Exit* actions are executed right before leaving the *state*, but after potential *entry* and *do* actions.
+In contrast to *do* actions, *exit* actions are always completely executed.
+
+- *Transitions* are denoted with a solid line and an open arrow.
+As the name implies, they are used to define *state transitions*.
+
 - *Composite states* are also denoted as rectangles with rounded corners and a name.
 They contain at least one *region*, i.e., a fragment that may execute concurrently with other *regions*.
 A single *region* in a composite state is not visible.